The development of distributed generators based on renewable energy may optimize energy structure, may promote energy conservation and emissions reduction, and may realize the economic sustainable development. In recent years, the distributed generators based on the renewable energy are grid-connected to promote the development of a micro-grid. The micro-grid is a micro power distribution system clustering distributed generators, an energy storage system, an energy conversion device, associated loads and a monitoring and protecting device. The micro-grid is an autonomous system being able to self-controlled, self-protected and self-managed. The micro-grid may not only to operate with an external power grid but may operate in isolation.
With more and more wind power generation and photovoltaic power generation being employed in the micro-grid, due to a frequency fluctuation, intermittency and uncertainty, as well as a rapid changing of the loads and a low inertia of the micro-grid, there is provided a severe challenge towards a controller for ensuring safety of the micro-grid in isolation.